food preservation

McGraw-Hill Science & Technology Dictionary:

food preservation

(′füd ′prez·ər′vā·shən)

(food engineering) Processing designed to protect food from spoilage caused by microbes, enzymes, and autooxidation.

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food preservation

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Any method by which food is protected against spoilage by oxidation, bacteria, molds, and microorganisms. Traditional methods include dehydration, smoking, salting, controlled fermentation (including pickling), and candying; certain spices have also long been used as antiseptics and preservatives. Among the modern processes for food preservation are refrigeration (including freezing), canning, pasteurization, irradiation, and the addition of chemical preservatives.

For more information on food preservation, visit Britannica.com.

McGraw-Hill Science & Technology Encyclopedia:

Food preservation

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The branch of food science and technology that deals with the practical control of factors capable of adversely affecting the safety, nutritive value, appearance, texture, flavor, and keeping qualities of raw and processed foods. Since thousands of food products differing in physical, chemical, and biological properties can undergo deterioration from such diverse causes as microorganisms, natural food enzymes, insects and rodents, industrial contaminants, heat, cold, light, oxygen, moisture, dryness, and storage time, food preservation methods differ widely and are optimized for specific products. See also Food science.

Food preservation methods involve the use of heat, refrigeration, freezing, concentration, dehydration, irradiation, pH control, chemical preservatives, and packaging applied to produce various degrees of preservation in accordance with the differing use patterns and shelf-life needs of unique products.

Thermal processes to preserve foods vary in intensity. True sterility to ensure total destruction of the most heat-resistant bacterial spores in nonacidic foods may require a treatment of at least 250°F (121°C) of wet heat for at least 15 min to be delivered throughout the entire food mass. The term commercial sterility refers to a less severe condition that still assures destruction of all pathogenic organisms, as well as organisms that, if present, could grow in the product and produce spoilage under normal conditions of handling and storage. See also Sterilization.

Many foods are subjected to still less severe heating by methods that produce pasteurization to assure destruction of pathogens and extend product shelf life. See also Pasteurization.

The slowing of biological and chemical activity with decreasing temperature is the principle behind cooling (refrigeration) and freezing preservation. In addition, when water is converted to ice, free water required for its solvent properties by all living systems is removed. Commercial freezing methods utilize refrigerated still air; high-velocity air, which is faster and more efficient; and high-velocity air made to suspend particulate foods, such as peas, as in a fluidized-bed fast freezer. Indirectcontact freezing utilizes hollow flat plates chilled with an internally circulated refrigerant to freeze solid foods, or with refrigerated tubular heat exchangers that rapidly slush-freeze liquids. Immersion freezing involves direct contact of the food or its container with refrigerants approved for food or a fast-freezing cryogenic liquid. See also Cold storage.

When sufficient water is removed from foods, microorganisms will not grow, and many enzymatic and nonenzymatic reactions will cease or be markedly slowed. Concentration preservation can be achieved by physically removing water, as by boiling or with lower-temperature vacuum evaporation, or by binding water through the addition of sugar, salt, or other solutes.

Foods preserved by dehydration contain considerably lower water activity and less total water than concentrated foods. Most dehydration methods utilize heat to vaporize and remove water. The heat and oxygen sensitivity of many foods necessitates vacuum dehydration for high quality. Under vacuum, water can be removed at reduced temperature, and oxidative changes are minimized. In freeze-drying, foods are frozen quickly and placed in a chamber under high vacuum. A food's structure remains rigid as it goes directly from the frozen state to dryness. See also Sublimation.

Food irradiation remains highly controversial, partly because of fears that the safety of products and processes cannot be adequately regulated. The natural acids of certain fruits and vegetables, acid added as a chemical, and acid produced by fermentation can inhibit or partially inhibit several pathogenic and spoilage organisms. The pH of acidic foods, however, is rarely sufficiently low to assure long-term preservation from acid alone. Many acidic and fermented foods further depend upon prior pasteurization of their ingredients, the addition of salt and other chemicals, and refrigeration. See also pH.

The U.S. Food and Drug Administration and comparable agencies in various countries vigorously regulate the chemicals that may be added to foods as well as the conditions of their use. Chemical preservatives and similar substances include antimicrobials, enzyme inhibitors, and antioxidants. There is much pressure to remove chemicals from the food supply, especially where their effects can be achieved by other means.

Packaging protects foods from contamination, moisture gain or loss, flavor loss and odor pickup, the adverse effects of light, physical damage, and intentional tampering. Ultimately, a food product's quality and storage life are determined largely by its package. See also Food engineering; Food manufacturing; Food microbiology.

Gale Encyclopedia of US History:

Food Preservation

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Food Preservation, protecting food from deterioration and decay so that it will be available for future consumption.

Natural Processes

Human beings learned to gather naturally preserved foods and to assist nature in the preserving process about 10,000 years ago, before the dawn of agriculture and animal husbandry. Human beings in the Stone Age stored nuts and seeds for winter use and discovered that meat and fish could be preserved by drying in the sun. After the discovery of fire, cooking made food more appetizing and was an aid to preservation, since heating killed some of the microorganisms and enzymes that caused spoilage. Smoking meat and fish as a means of preservation grew out of cooking. After farming developed—the Neolithic Period, or New Stone Age—human beings had more dependable surpluses for preservation. Native Americans subsisted on dry corn and beans that they had stored for winter use; Plains Indians cut buffalo meat into thin strips and dried it in the sun on wooden frames.

Salt was used for flavoring before it was learned that meat soaked in salt brine or rubbed with salt would keep for weeks or months. Brining, later called "pickling," became a favorite way to keep fruits and vegetables for winter use. Sugar was used as a preservative in ancient times, and making jam and marmalade was widely practiced. While spices were thought to preserve food, they mainly served to cover up unpleasant flavors.

Fermentation, the natural process of chemical change in food, was observed, probably by chance, and used thousands of years ago. Fermented fruit juices resulted in wine, a safe beverage in areas of uncertain water supply. Brewing came later. Another product of fermentation, vinegar, was useful for pickling meats, fish, fruits, and vegetables. The Chinese, and later the Germans and other Europeans, fermented cabbage or sauerkraut. About three thousand years ago milk, which does not keep well, was first fermented into cheese. About the same time, Egyptians developed raised sourdough bread, another result of fermentation. In some areas and during some parts of the year, people preserved food by freezing it, but thousands of years passed before freezing became available through man-made processes in all parts of the world throughout the year.

Processes Created by Humans

Canning. Until the nineteenth century human beings were dependent on the natural processes of drying, cooking, salting, pickling, fermenting, and freezing for food preservation. These had been only slightly modified over the ages. Then, in the early 1800s a French chemist and confectioner, Nicolas Appert, developed canning, for which he was awarded a prize by his government in 1809. Although a theoretical understanding of the benefits of canning did not come until Louis Pasteur observed the relationships between microorganisms and food spoilage some fifty years later, Appert's ideas were still valid. He placed wholesome food in clean metal containers, which were then sealed and boiled long enough to kill the spoilage-causing microorganisms.

Canning spread rapidly. In 1810 an Englishman, Peter Durand, patented a can of iron coated with tin. Today's cans are primarily steel, with a thin coating of tin and, usually, an enamel lining. Commercial canning began in the United States with pickles and ketchup in Boston in 1819 and seafood in Baltimore in 1820. The cooking in boiling water took five or six hours in the early days, but this was sharply reduced in 1860 when Isaac Solomon added calcium chloride to the water, raising its boiling point. The introduction of the pressure cooker, or retort, in 1874 was an even more important step, permitting much more rapid processing. Commercial canners then turned to machines that would do many of the tasks formerly done by hand, such as shelling peas, cutting corn from the cob, and cleaning salmon.

After 1900, enthusiasts of domestic science, agents of agricultural extensions, and others encouraged home canning of all types of food, mainly in glass jars, as a means of utilizing home garden products, providing better diets, and reducing the cost of living on farms. By the early 2000s the decline of the family farm, the low cost of commercially canned foods, and the widespread use of freezers had made home canning rare.

Drying. A sizable dried-fruit industry flourished in the United States long before the arrival of mechanical refrigeration. In colonial times great quantities of apples were dried in the sun and by artificial means. Prior to 1795 drying and the use of salt and sugar were the principal methods of preserving foods. In 1854, it was estimated, Maine could furnish the nation's supply of dried apples. The perfection of fruit evaporators in 1870–1875 increased exports of dried-fruit products. Thirty million pounds of dried apples were exported in 1880. Of nearly a half-billion pounds of dried apples exported in 1909, 83 percent came from California. Later, new drying processes and machinery enlarged outputs for domestic and foreign markets. Meanwhile, refrigeration and canning developed vastly to aid drying in preserving fruit, vegetables, meat, and other foods for human consumption. New methods of preserving foods in their fresh state reduced the need for dried foods, which became high-priced delicacies, served as appetizers or candied.

Refrigeration and freezing. As a means of commercial food preservation, refrigeration preceded freezing. In 1803 Thomas Moore, a Maryland dairy farmer who lived about twenty miles from Washington, D.C., began transporting butter to the new capital city in an icebox of his own design, getting a premium price for his product. Moore patented his refrigerator and published a pamphlet describing it. By the 1840s, American families were beginning to use iceboxes for food storage and preservation. One of the first recorded refrigerated rail shipments was a load of butter, packed in ice and shipped from Ogdensburg, N.Y., to New York City in 1851. In 1868 William Davis patented a refrigerator car with metal tanks along the sides that were filled with ice from the top.

Beginning in the 1830s, various systems of mechanical refrigeration were patented in the United States. Eventually both freight cars and trucks with mechanical refrigeration were developed. In the home the mechanical refrigerator began to replace the icebox in the 1920s. Mechanical refrigeration made possible another major advance in food preservation—freezing. This process decentralized storage and improved the taste and nutritive value of storable foods. In 1912 Clarence Birdseye, a graduate of Amherst College, was in Labrador and noticed that freshly caught fish pulled through the ice quickly froze solid. When thawed, the fish might revive because quick freezing prevented large ice crystals from forming and thus avoided the breakage of cell walls. The physical character of the tissue, and incidentally its taste, remained the same. After much experimentation, Birdseye invented a machine for quick-freezing food products. The machine froze by conduction—that is, by pressing the food directly between very cold metal plates. In 1923 Birdseye established a frozen seafood company that was eventually successful.

Frozen concentrated orange juice, based on a process developed in the U.S. Department of Agriculture, became widely used after World War II. The freezing process also permitted the marketing of precooked food, sold ready to heat and serve. As frozen foods became more prevalent, deep-freeze compartments were included in many home refrigerators. Central frozen-food lockers became popular in many small towns and were widely used to preserve meat. After World War II frozen foods became even more popular and many families began purchasing separate deep-freeze units. These could be used for freezing home-produced foods or for storing commercially prepared products. By 1973 one household in three had its own deep-freeze unit; by the end of the century virtually all full-size domestic refrigerators included freezers.

Quick freezing led to the development of another means for preserving food—freeze drying. World War II supplied a strong impetus to the development of improved methods of drying food. In general the problem was to dry quickly without heat damage. Spray drying was particularly helpful in improving the quality of dried eggs and powdered milk. Other methods of drying produced potatoes, soup mixes, fruit juices, and other items that could be conveniently shipped and stored before being reconstituted for consumption. Freeze drying developed after World War II. In this process the product is frozen and the moisture is then removed as a vapor by sublimation. The resulting food, after reconstitution, retains much of its original flavor, color, and texture. By the 1970s freeze drying was widely used for coffee, soup mixes, and other dehydrated convenience foods. Some meat was freeze dried, and other developments kept meats edible for prolonged periods of time. Antibiotics introduced into chilling tanks, for example, prolonged the freshness of poultry.

Irradiation. The late–twentieth century saw the emergence of irradiation, or radurization, a pasteurization method in which food is exposed to low levels of high-energy ionizing radiation in an effort to kill microbial contaminants. If properly refrigerated and packaged, irradiated meat, fruit, and vegetable products enjoyed a significantly extended storage life. However, because of inherent concerns about radiation, and the tendency of irradiated foods to lose some of their nutritional value, irradiation was used only sparingly. Scientists, consumer groups, and the food industry continued to debate its effectiveness.

Bibliography

Anderson, Oscar E. Refrigeration in America. Port Washington, N.Y.: Kennikat Press, 1972.

David, Elizabeth. Harvest of the Cold Months: The Social History of Ice and Ices. Edited by Jill Norman. New York: Viking, 1994.

Woolrich, Willis R. The Men Who Created Cold: A History of Refrigeration. New York: Exposition Press, 1967.

—Louis Pelzer

Columbia Encyclopedia:

food preservation

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food preservation, methods of preparing food so that it can be stored for future use. Because most foods remain edible for only a brief period of time, people since the earliest ages have experimented with methods for successful food preservation. Among the products of early food conservation were cheese and butter, raisins, pemmican, sausage, bacon, and grain.

As scientific investigations regarding the causes of food spoilage were undertaken, they pointed the way to a wider application of methods already in use and to the discovery of new ones. Before 1860 changes in food were explained on the theory of spontaneous generation. Pasteur demonstrated that ferments, molds, and some forms of putrefaction were caused by the presence of microorganisms widely distributed in the environment. Since these microorganisms are the main cause of food spoilage, food preservation depends on rendering conditions unfavorable for their growth. Processes of preservation may be generally classified as drying, heating, refrigeration (see also frozen foods), and the use of chemicals or other particular agencies.

Drying and Heating

The most ancient method is drying, and it was employed early for fruits, grains, vegetables, fish, and meat. It was sometimes combined with parching, as in the oatmeal of Scotland or the corn of the Native American. Modern applications of this ancient device are seen in dried or dehydrated fruits and vegetables, milk, meat, and eggs. A more recent variation, known as freeze-drying, is now being used on such foods as instant coffee, meat, orange juice, and soup. The early method of drying was by direct exposure to the sun's rays; in modern industry the process is hastened by complex apparatus and by chemical agencies. The use of sugar was early combined with drying. Smoking, a method used mainly for fish and meat, combines the drying action with chemicals produced from the smoke, which form a protective coating. The process of heating was used centuries before its action was understood (see canning). One of the most important modern applications of the heat principle is the pasteurization of milk.

Preservatives

In modern food preservation, preservatives function in two ways. One is by delaying the spoilage of the food, while the other is by ensuring that the food retains, as nearly as possible, its original quality. The first method includes the use of sugar (see jelly and jam), vinegar for pickling meats and vegetables, salt (one of the oldest preservatives), and alcohol. Good wine will keep almost indefinitely, and fruit placed in a 15% to 20% alcohol solution (brandying) is well preserved. The second method includes the use of ascorbic acid (which prevents color deterioration in canned fruits), benzoic acid, sulfur dioxide, and a variety of neutralizers, firming agents, and bleaching agents. The excessive or unacknowledged use of these chemical agencies has been legislated against by most governments.

Exclusion of Air

The exclusion of air, nowadays accomplished by hermetic sealing, is an old device, formerly practiced by pouring hot oil over potted meat or fish, by coating or mixing food with melted fat, as in pemmican, or by burying vegetables in the earth or in sand. The use of melted paraffin achieves the same result. Eggs may be preserved by preventing air from penetrating their porous shells, usually by coating them with an impervious substance.

Irradiation

Irradiation has also been used successfully to destroy many of the microorganisms that might cause spoilage in food. Irradiation has been declared safe by the Food and Drug Administration and World Health Organization. Thus, despite opposition from those who fear that health hazards from its use will be discovered later, this method is gradually gaining acceptance.

Bibliography

See G. Borgstrom, Principles of Food Science (2 vol., 1968); N. W. Desrosier, The Technology of Food Preservation (3d ed. 1970); S. Thorne, The History of Food Preservation (1986).

Wikipedia on Answers.com:

Food preservation

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Canadian World War I poster encouraging people to preserve food for the winter.

Various preserved foods

Food preservation is the process of treating and handling food to stop or slow down spoilage (loss of quality, edibility or nutritional value) and thus allow for longer storage.

Preservation usually involves preventing the growth of bacteria, yeasts, fungi, and other micro-organisms (although some methods work by introducing benign bacteria, or fungi to the food), as well as retarding the oxidation of fats which cause rancidity. Food preservation can also include processes which inhibit visual deterioration that can occur during food preparation; such as the enzymatic browning reaction in apples after they are cut.

Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit, by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). There are many traditional methods of preserving food that limit the energy inputs and reduce carbon footprint.^[1]

Maintaining or creating nutritional value, texture and flavour is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. In many cases these changes have now come to be seen as desirable qualities – cheese, yoghurt and pickled onions being common examples.

Preservation processes

Preservation processes include:^{[citation needed]}

Heating to kill or denature micro-organisms (e.g., boiling)
Oxidation (e.g., use of sulfur dioxide)
Ozonation (e.g., use of ozone [O3] or ozonated water to kill undesired microbes)
Toxic inhibition (e.g., smoking, use of carbon dioxide, vinegar, alcohol etc.)
Dehydration (drying)
Osmotic inhibition (e.g., use of syrups)
Low temperature inactivation (e.g., freezing)
Ultra high water pressure (e.g. a type of “cold” pasteurization; intense water pressure kills microbes which cause food deterioration and affect food safety)
Combinations of these methods

Drying

A collection of dried mushrooms

Main article: Drying (food)

Drying is one of the most ancient food preservation techniques,^[2] which reduces water activity sufficiently to prevent or delay bacterial growth.

Refrigeration

Main article: Refrigerator#Commercial and domestic refrigerators

Refrigeration preserves food by slowing down the growth and reproduction of micro-organisms and the action of enzymes which cause food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the Western world by allowing foods such as fresh fruit, salads and dairy products to be stored safely for longer periods, particularly during warm weather.

Freezing

Pictorial guide inside a freezer door

Main article: Frozen food

Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food including prepared food stuffs which would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores provide large volume, long-term storage for strategic food stocks held in case of national emergency in many countries.

Vacuum packing

Main article: Vacuum packing

Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival, slowing spoiling. Vacuum-packing is commonly used for storing nuts to reduce loss of flavor from oxidation.

Salt

Bag of Prague powder #1, also known as "curing salt" or "pink salt." It's typically a combination of salt and sodium nitrite, with the pink color added to distinguish it from ordinary salt.

Main article: Curing (food preservation)

Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat and contribute the characteristic pink color, as well as inhibition of Clostridium botulinum.

Sugar

Main article: Sugaring

Sugar is used to preserve fruits, either in syrup with fruit such as apples, pears, peaches, apricots, plums or in crystallized form where the preserved material is cooked in sugar to the point of crystallisation and the resultant product is then stored dry. This method is used for the skins of citrus fruit (candied peel), angelica and ginger. A modification of this process produces glacé fruit such as glacé cherries where the fruit is preserved in sugar but is then extracted from the syrup and sold, the preservation being maintained by the sugar content of the fruit and the superficial coating of syrup. The use of sugar is often combined with alcohol for preservation of luxury products such as fruit in brandy or other spirits. These should not be confused with fruit flavored spirits such as cherry brandy or Sloe gin.

Smoking

Main article: Smoking (cooking)

Smoking is used to lengthen the shelf life of perishable food items. This effect is achieved by exposing the food to smoke from burning plant materials such as wood. Most commonly subjected to this method of food preservation are meats and fish that have undergone curing. Fruits and vegetables like paprika, cheeses, spices, and ingredients for making drinks such as malt and tea leaves are also smoked, but mainly for cooking or flavoring them. It is one of the oldest food preservation methods, which probably arose after the development of cooking with fire.

Artificial food additives

Main article: Preservatives#Preservatives in foods

Preservative food additives can be antimicrobial; which inhibit the growth of bacteria or fungi, including mold, or antioxidant; such as oxygen absorbers, which inhibit the oxidation of food constituents. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.) and disodium EDTA. Antioxidants include BHA and BHT. Other preservatives include formaldehyde (usually in solution), glutaraldehyde (kills insects), ethanol and methylchloroisothiazolinone.

Pickling

Main article: Pickling

Pickling is a method of preserving food in an edible anti-microbial liquid. Pickling can be broadly categorized as chemical pickling for example, In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other micro-organisms. Typical pickling agents include brine (high in salt), vinegar, alcohol, and vegetable oil, especially olive oil but also many other oils. Many chemical pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Common chemically pickled foods include cucumbers, peppers, corned beef, herring, and eggs, as well mixed vegetables such as piccalilli.

In fermentation pickling, the food itself produces the preservation agent, typically by a process that produces lactic acid. Fermented pickles include sauerkraut, nukazuke, kimchi, surströmming, and curtido. Some pickled cucumbers are also fermented.

In commercial pickles, a preservative like sodium benzoate or EDTA may also be added to enhance shelf life.

Lye

Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Lye will saponify fats in the food, which will change its flavor and texture. Lutefisk uses lye in its preparation, as do some olive recipes. Modern recipes for century eggs also call for lye. Masa harina and hominy use agricultural lime in their preparation and this is often misheard as 'lye'.

Canning and bottling

Spam is a canned and preserved meat product.

Preserved food

Main article: Canning

Jellying

Main article: Aspic

Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include gelatine, agar, maize flour and arrowroot flour. Some foods naturally form a protein gel when cooked such as eels and elvers, and sipunculid worms which are a delicacy in the town of Xiamen in Fujian province of the People's Republic of China. Jellied eels are a delicacy in the East End of London where they are eaten with mashed potatoes. Potted meats in aspic, (a gel made from gelatine and clarified meat broth) were a common way of serving meat off-cuts in the UK until the 1950s. Many jugged meats are also jellied.

Potting

Further information: Potted meat

Jugging

Main article: Jugging

Meat can be preserved by jugging, the process of stewing the meat (commonly game or fish) in a covered earthenware jug or casserole. The animal to be jugged is usually cut into pieces, placed into a tightly-sealed jug with brine or gravy, and stewed. Red wine and/or the animal's own blood is sometimes added to the cooking liquid. Jugging was a popular method of preserving meat up until the middle of the 20th century.

Irradiation

Main article: Food irradiation

Irradiation of food^[4] is the exposure of food to ionizing radiation; either high-energy electrons or X-rays from accelerators, or by gamma rays (emitted from radioactive sources as Cobalt-60 or Caesium-137). The treatment has a range of effects, including killing bacteria, molds and insect pests, reducing the ripening and spoiling of fruits, and at higher doses inducing sterility. The technology may be compared to pasteurization; it is sometimes called 'cold pasteurization', as the product is not heated. Irradiation is not effective against viruses or prions, it cannot eliminate toxins already formed by microorganisms, and is only useful for food of high initial quality.

The radiation process is unrelated to nuclear energy, but it may use the radiation emitted from radioactive nuclides produced in nuclear reactors. Ionizing radiation is hazardous to life (hence its usefulness in sterilisation); for this reason irradiation facilities have a heavily shielded irradiation room where the process takes place. Radiation safety procedures ensure that neither the workers in such facility nor the environment receive any radiation dose from the facility. Irradiated food does not become radioactive, and national and international expert bodies have declared food irradiation as wholesome. However, the wholesomeness of consuming such food is disputed by opponents^[5] and consumer organizations.^[6] National and international expert bodies have declared food irradiation as 'wholesome'; UN-organizations as WHO and FAO are endorsing to use food irradiation. International legislation on whether food may be irradiated or not varies worldwide from no regulation to full banning.^[7] Irradiation may allow lower quality or contaminated foodstuffs to be rendered marketable.

It is estimated that about 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly spices and condiments with an increasing segment of fresh fruit irradiated for fruit fly quarantine.^[8]^[9]

Pulsed electric field processing

Pulsed electric field (PEF) processing is a method for processing cells by means of brief pulses of a strong electric field. PEF holds potential as a type of low temperature alternative pasteurization process for sterilizing food products. In PEF processing, a substance is placed between two electrodes, then the pulsed electric field is applied. The electric field enlarges the pores of the cell membranes which kills the cells and releases their contents. PEF for food processing is a developing technology still being researched. There have been limited industrial applications of PEF processing for the pasteurization of fruit juices.

Modified atmosphere

Main article: Modified atmosphere

Modifying atmosphere is a way to preserve food by operating on the atmosphere around it. Salad crops which are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O₂) concentration and increase the carbon dioxide (CO₂) concentration. There is concern that although salad vegetables retain their appearance and texture in such conditions, this method of preservation may not retain nutrients, especially vitamins. Grains may be preserved using carbon dioxide by one of two methods; either using a block of dry ice placed in the bottom and the can is filled with grain or the container can be purged from the bottom by gaseous carbon dioxide from a cylinder or bulk supply vessel.

Carbon dioxide prevents insects, and depending on concentration, mold, and oxidation from damaging the grain. Grain stored in this way can remain edible for five years.^{[citation needed]}

Nitrogen gas (N₂) at concentrations of 98% or higher is also used effectively to kill insects in grain through hypoxia.^[10] However, carbon dioxide has an advantage in this respect as it kills organisms through hypercarbia and depending on concentration hypoxia and, requiring concentrations of above 35%,^[11] or so. This makes carbon dioxide preferable for fumigation in situations where a hermetic seal cannot be maintained.

Air-tight storage of grains (sometimes called hermetic storage) relies on the respiration of grain, insects and fungi which can modify the enclosed atmosphere sufficiently to control insect pests. This is a method of great antiquity ^[12], as well as having modern equivalents. The success of the method relies on have the correct mix of sealing, grain moisture and temperature ^[13].

High pressure food preservation

Main article: High pressure food preservation

High pressure food preservation refers to high pressure used for food preservation. "Pressed inside a vessel exerting 70,000 pounds per square inch (480 MPa) or more, food can be processed so that it retains its fresh appearance, flavour, texture and nutrients while disabling harmful microorganisms and slowing spoilage. By 2005 the process was being used for products ranging from orange juice to guacamole to deli meats and widely sold.^[14]

Burial in the ground

Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or desiccants in the soil. Burial may be combined with other methods such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty (thus a desiccant), or soil that is frozen.

Many root vegetables are very resistant to spoilage and require no other preservation than storage in cool dark conditions, for example by burial in the ground, such as in a storage clamp. Century eggs are created by placing eggs in alkaline mud (or other alkaline substance) resulting in their "inorganic" fermentation through raised pH instead of spoiling. The fermentation preserves them and breaks down some of the complex, less flavorful proteins and fats into simpler more flavorful ones. Cabbage was traditionally buried in the fall in northern farms in the USA for preservation. Some methods keep it crispy while other methods produce sauerkraut^{[citation needed]}. A similar process is used in the traditional production of kimchi. Sometimes meat is buried under conditions which cause preservation. If buried on hot coals or ashes, the heat can kill pathogens, the dry ash can desiccate, and the earth can block oxygen and further contamination. If buried where the earth is very cold, the earth acts like a refrigerator.

Controlled use of micro-organism

Biopreservation

3D stick model of nisin. Some lactic acid bacteria manufacture nisin. It is a particularly effective preservative

Main article: Biopreservation

Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of preserving food and extending its shelf life.^[15] Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food.^[16] It is a benign ecological approach which is gaining increasing attention.^[15]

Of special interest are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties which make them particularly useful as biopreservatives. When LABs compete for nutrients, their metabolites often include active antimicrobials such as lactic and acetic acid, hydrogen peroxide, and peptide bacteriocins. Some LABs produce the antimicrobial nisin which is a particularly effective preservative.^[17]^[18]

These days LAB bacteriocins are used as an integral part of hurdle technology. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibiting the activities of a wide spectrum of organisms, including inherently resistant Gram-negative bacteria.^[15]

Hurdle technology

Main article: Hurdle technology

Hurdle technology is a method of ensuring that pathogens in food products can be eliminated or controlled by combining more than one approach. These approaches can be thought of as "hurdles" the pathogen has to overcome if it is to remain active in the food. The right combination of hurdles can ensure all pathogens are eliminated or rendered harmless in the final product.^[19]

Hurdle technology has been defined by Leistner (2000) as an intelligent combination of hurdles which secures the microbial safety and stability as well as the organoleptic and nutritional quality and the economic viability of food products.^[20] The organoleptic quality of the food refers to its sensory properties, that is its look, taste, smell and texture.

Examples of hurdles in a food system are high temperature during processing, low temperature during storage, increasing the acidity, lowering the water activity or redox potential, or the presence of preservatives or biopreservatives. According to the type of pathogens and how risky they are, the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without sacrificing the safety of the product.^[19]

Principal hurdles used for food preservation (after Leistner, 1995)^[21]^[22]
Parameter	Symbol	Application
High temperature	F	Heating
Low temperature	T	Chilling, freezing
Reduced water activity	a_w	Drying, curing, conserving
Increased acidity	pH	Acid addition or formation
Reduced redox potential	E_h	Removal of oxygen or addition of ascorbate
Biopreservatives		Competitive flora such as microbial fermentation
Other preservatives		Sorbates, sulfites, nitrites

Notes

^ "Preserving Food without Freezing or Canning, Chelsea Green Publishing, 1999"
^ "Historical Origins of Food Preservation." University of Georgia, National Center for Home Food Preservation. Accessed June 2011.
^ Nicolas Appert inventeur et humaniste by Jean-Paul Barbier, Paris, 1994 and http://www.appert-aina.com
^ anon., Food Irradation - A technique for preserving and improving the safety of food, WHO, Geneva, 1991
^ Hauther,W. & Worth, M., Zapped! Irradiation and the Death of Food, Food & Water Watch Press, Washington, DC, 2008
^ Consumers International - Home
^ NUCLEUS - Food Irradiation Clearances
^ Food irradiation - Position of ADA J Am Diet Assoc. 2000;100:246-253
^ C.M. Deeley, M. Gao, R. Hunter, D.A.E. Ehlermann, The development of food irradiation in the Asia Pacific, the Americas and Europe; tutorial presented to the International Meeting on Radiation Processing, Kuala Lumpur, 2006. http://www.doubleia.org/index.php?sectionid=43&parentid=13&contentid=494
^ Annis, P.C. and Dowsett, H.A. 1993. Low oxygen disinfestation of grain: exposure periods needed for high mortality. Proc. International Conference on Controlled Atmosphere and Fumigation. Winnipeg, June 1992, Caspit Press, Jerusalem, pp 71-83.
^ Annis, P.C. and Morton, R. 1997. The acute mortality effects of carbon dioxide on various life stages of Sitophilus oryzae. J. Stored Prod.Res. 33. 115-124
^ Various authors, Session 1: Natural Air-Tight Storage In: Shejbal, J., ed., Controlled Atmosphere Storage of Grains, Elsevier: Amsterdam, 1-33
^ Annis P.C. and Banks H.J. 1993. Is hermetic storage of grains feasible in modern agricultural systems? In “Pest control and sustainable agriculture” Eds S.A. Corey, D.J. Dall and W.M. Milne. CSIRO, Australia. 479-482
^ "High-Pressure Processing Keeps Food Safe". Military.com. Archived from the original on 2008-02-02. http://web.archive.org/web/20080202232043/http://www.military.com/soldiertech/0,14632,Soldiertech_Squeeze,,00.html. Retrieved 2008-12-16. "Pressed inside a vessel exerting 70,000 pounds per square inch or more, food can be processed so that it retains its fresh appearance, flavor, texture and nutrients while disabling harmful microorganisms and slowing spoilage."
^ ^a ^b ^c Ananou S, Maqueda M, Martínez-Bueno M and Valdivia E (2007) "Biopreservation, an ecological approach to improve the safety and shelf-life of foods" In: A. Méndez-Vilas (Ed.) Communicating Current Research and Educational Topics and Trends in Applied Microbiology, Formatex. ISBN 9788461194230.
^ Yousef AE and Carolyn Carlstrom C (2003) Food microbiology: a laboratory manual Wiley, Page 226. ISBN 9780471391050.
^ FAO: Preservation techniques Fisheries and aquaculture department, Rome. Updated 27 May 2005. Retrieved 14 March 2011.
^ Alzamora SM, Tapia MS and López-Malo A (2000) Minimally processed fruits and vegetables: fundamental aspects and applications Springer, Page 266. ISBN 9780834216723.
^ ^a ^b Alasalvar C (2010) Seafood Quality, Safety and Health Applications John Wiley and Sons, Page 203. ISBN 9781405180702.
^ Leistner I (2000) "Basic aspects of food preservation by hurdle technology" International Journal of Food Microbiology, 55:181–186.
^ Leistner L (1995) "Principles and applications of hurdle technology" In Gould GW (Ed.) New Methods of Food Preservation, Springer, pp. 1-21. ISBN 9780834213418.
^ Lee S (2004) "Microbial Safety of Pickled Fruits and Vegetables and Hurdle Technology" Internet Journal of Food Safety, 4: 21-32.

References

Riddervold, Astri. Food Conservation. ISBN 9780907325406.

External links

Wikimedia Commons has media related to: Food preservation

Dehydrating Food
Preserving foods ~ from the Clemson Extension Home and Garden Information Center
National Center for Home Food Preservation
BBC News Online - US army food... just add urine
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An e-book collection of over 1,000 classic books on home economics spanning 1850 to 1950, created by Cornell University's Mann Library.

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